1. Field of the Invention
The present general inventive concept relates to an electrophotographic toner and a method of preparing the same, and more particularly, to an electrophotographic toner including wax and a binder which are appropriately distributed and thus have improved liquidity and durability characteristics and can be preserved for a long period of time without an occurrence of offsets, and a method of preparing the same.
2. Description of the Related Art
Electrophotographic techniques and electrostatic recording techniques use developers that visualize electrostatic images or electrostatic latent images. Developers can be categorized into two-component developers and one-component developers. Two-component developers include toner and carrier particles. One-component developers only include toner. One-component developers can be sub-categorized into magnetic one-component developers that contain a magnetic component and non-magnetic one-component developers that do not contain a magnetic component. Non-magnetic one-component developers generally include a fluidizer to increase a fluidity of the toner. The fluidizer can be colloidal silica. In general, toner refers to color particles that are prepared by dispersing a pigment such as carbon black and additives in latex and forming the dispersion product into particles.
Toner can be prepared by using a grinding method or a polymerizing method. In the grinding method, a synthesized resin, a pigment, and if necessary, additives are dissolved and mixed. The mixture is then ground and the resultant particles are classified in order to obtain particles having a desired diameter. In the polymerizing method of a polymerization toner, a polymerizable monomer, a pigment, a polymerization initiator, and if necessary, additives, such as a crosslinking agent or an antistatic agent, are homogeneously dissolved or dispersed to form a polymerizable monomer composition. The polymerizable monomer composition is then dispersed with an agitator in an aqueous dispersion medium containing a dispersion stabilizer so as to form droplet particles of the polymerizable monomer composition. Then the temperature of the mixture is increased and a suspension-polymerization process is performed thereon in order to obtain color polymerization particles having desired particle diameters.
Meanwhile, image forming apparatuses, such as an electrophotographic apparatus or an electrostatic recording apparatus, form an image by using the following method. First, a homogeneously charged photoreceptor is exposed to light and a latent image is formed. Then, toner is attached to the latent image to form a toner image. The toner image is then transferred to a transfer medium such as a transfer sheet. Then, the un-fixed toner image is fixed onto the transfer medium by, for example, heating, pressing, or solvent evaporating. In the fixing process, in general, the transfer medium onto which the toner image is transferred passes between a fixing roll and a pressing roll and toner of the toner image is heated and pressed, so that the toner image is thereby fused onto the transfer medium.
Some image forming apparatuses, such as electrical photocopiers, require accurate and precise image forming characteristics. Conventionally, toner used in an image forming apparatus is prepared by using a grinding method. However, when the grinding method is used, the obtained toner particles have a wide particle-diameter distribution. Therefore, in order to obtain appropriate development characteristics, the toner particles need to be sorted or classified to reduce the particle-diameter distribution. However, when toner particles for an electrophotographic technique or an electrostatic technique are prepared by using conventional mixing and grinding processes, it is difficult to accurately control particle diameters and the distribution of particle diameters, and thus the yield of small particles is low due to the need for the classification process. In addition, there is a limitation on modification/adjustment of the toner design for improving charging and fixing characteristics. Meanwhile, for polymerization toner, particle diameters can be easily controlled, and complex processes, such as a sorting or a classifying process, are not used. Due to these advantages, polymerization toner is receiving much attention.
As described above, when toner is prepared by using a polymerizing process, polymerization toner having desirable particle diameters and desirable particle-diameter distribution can be obtained without grinding or a classifying process. However, it is still difficult to obtain a uniform particle diameter and a uniform particle shape. That is, toner particles having particle diameters outside a center of a particle size distribution can be easily controlled, but particles having small diameters have a higher level of circularity than a desired circularity level. In addition, for electrophotographic processes, problems may arise when a blade is cleaned.
Furthermore, for toner to have high gloss levels and wide fixing regions, the toner may be prepared in a capsule-like shape by using a coagulation process. Certainly, by controlling a shape of the toner, surface exposure of a pigment and a wax is prevented, and uniform charging, high liquidity, and high thermal preservation can be obtained. An anti-offset characteristic of the toner is considered as an important factor when it comes to a stable fixing region. To obtain the anti-offset characteristic, silicon oil can be coated on a fixing roller. However, when oil is applied, an oil tank and other devices are further needed, a fixing roller may deteriorate, or maintenance may need to be performed frequently. To prevent the fusing phenomenon of the toner, in general, wax can be added to the toner to provide a releasing effect. The releasing effect is significantly dependent on distribution states of a wax and a binder.
Meanwhile, if the distribution of wax on a toner surface is high, liquidity, and charging characteristics are degraded and durability is decreased. On the other hand, if wax is inappropriately distributed in a binder and is located inside a toner, the wax may fail to perform its due function as a releasing agent, high-temperature offsets may occur, and gloss levels may be decreased, and thus, stable image quality cannot be obtained.